1. Field of the Invention
This invention relates to a vacuum switch tube and more particularly to a vacuum switch tube having an internal hollow cylindrical metallic protection screen surrounding internal switch contacts.
2. Description of the Prior Art
It is known to provide a vacuum switch tube with a hollow cylinder insulating member which is vacuum sealed at the end by metallic flanges carrying contacts for the switch tube. A cylindrical insulator member is provided with a circumferential inner groove at a center portion wherein a ring-shaped metallic mounting may be arranged to carry a hollow cylinder metallic protection screen which is spaced from the inner insulating member wall and surrounds the switch contacts concentrically.
Such a vacuum switch tube is known from the U.S. Pat. No. 3,857,005 (German Offenlegungsschrift No. 2,058,020). This publication, however, provides no teaching as to an appropriate arrangement and mounting of the metallic protection screen within the vacuum switch tube interior.
It is also known in the art such as from German Letters Pat. No. 1,267,305 (U.S. Patent Application Ser. No. 424,600) to mount the mounting ring of the vapor screen by way of hard soldering between a divided ceramic cylinder or by way of a welding method applied between two metal flanges attached by way of glazing (see German Auslegeschrift No. 1,245,472). Finally it is also known from U.S. Pat. No. 3,283,103 (German Auslegeschrift No. 1,273,661) to protect the insulating inner surfaces of the vacuum tight switch housing from the precipitation of metal particles produced by the light arc by use of a tubular metal screen. The screen catches the metal vapors emanating from the light arc during switching processes and condenses them before they reach the wall of the housing thereby preventing any degradation of the insulating effects of the walls. Again, however, this publication does not make any explicit statements concerning the attachment of the metal screen. It merely states that the metal screen is mounted to the housing in a suitable manner.